The leader of Thailand's junta could become prime minister in a government to be set up under a newly drafted interim constitution, a junta legal adviser says.

However the nomination will be decided by an appointed provisional parliament.

The military has ruled Thailand since a coup on May 22 and analysts say General Prayuth Chan-ocha, who leads the ruling military council, could remain the country's leader until a general election, tentatively due in the second half of 2015.

Asked at a news conference on the interim charter whether General Prayuth would be prime minister, Wissanu Krea-ngam, a legal adviser to the junta, said: "The constitution allows it, but whether he is appointed or not is down to the National Legislative Assembly."

Thai king endorses military's interim constitution

On Tuesday, Thailand's king endorsed an interim constitution that grants power to the military to intervene in politics for security reasons without approval of a civilian government.

The constitution maintains the power of the National Council for Peace and Order (NCPO), or the junta, that has ruled Thailand since a coup on May 22.

It also grants immunity from prosecution to those who led the revolt.

The draft gave no timeframe for when an election would take place, although junta leader General Prayuth Chan-ocha has said it would likely come at the end of next year.

The NCPO would hand-pick members of a temporary parliament, which would appoint an interim prime minister.

But the constitution did not state when that would happen.

The charter was whittled down from 309 articles to just 48 and allows the NCPO to intervene in matters it deems "destructive to the peace and safety of the country" even if the that meant disrupting the interim government's work.

The military said its coup was to restore order after months of unrest as protesters tried to topple former Prime Minister Yingluck Shinawatra.

Ms Yingluck is the sister of tycoon Thaksin Shinawatra, an ex-premier whose parties have won every election since 2001 on a groundswell of working-class support.

Ms Yingluck was forced to step down by a court on May 7 for abuse of power and the remainder of her caretaker cabinet was ousted by the army two weeks later.